Hydraulically actuated boat hoists are shown in U.S. Pat. No. 6,823,809 to Hey, U.S. Pat. No. 6,976,442 to Hey U.S. Pat. No. 7,246,970 to Hey, U.S. Pat. No. 7,413,378 to Way and U.S. Pat. No. 8,267,621 to Way, all of which are incorporated herein by reference in their entirety.
Southern U.S. States and coastal regions commonly use one of these three methods to store/moor boats: (1) Moor the boat to a fixed or floating pier using ropes. In this case, the boat remains in the water, (2) lift the boat using a platform or sling type lift mounted to a set of pilings or roof structure mounted on pilings, or (3) lift the boat using a floating lift system. The most common method used depends on the region and regulations governing the body of water. Many reservoirs do not allow private ownership of waterfront property. In these lakes, there tends to be large marinas or “dockominum” structures. In these structures in-water mooring is the most common. A small percentage of the boats are lifted using a floating lift. Floating lifts are usually the only type allowed on a large dock structure. Marina managers discourage any structure being fixed to these floating systems.
Many lakes and waterways allow private waterfront ownership. In these cases, a permanent, fixed pier can be installed. Often a permanent roof structure is built over the slip intended for the boat commonly called a “boat house”. When these structures are present, a large percentage will have a mounted lift system. Some permanent docks do not have a roof structure. A lift is usually mounted on the top of large pilings when no roof is present.
Pile and roof mounted lift systems have been around for decades. The lift designs are basically the same. Galvanized poles are mounted in bearings hanging from a beam in the roof or a beam mounted along the pilings. A “plate-gear” motor is connected to the end of the pole that causes the entire pole to turn. Cables are attached to the pole and wind as the pole turns. In lower capacity, roof-mount applications, one pole can be used, but in pile mount applications and higher capacity roof-mounts, two poles and motors are used.
Some differentiation exists in the pole winding products. Some have improved on the motor and controls to included wireless operation. Some have added machined cable grooves to improve cable winding. There is even one company that uses a “level cable” technique to make a single motor/pole piling application. They also have some variation on the platform, bunks, and load guide features. Low-cost kits use a sling instead of a platform.
Pole-winders have many weaknesses that present opportunities. Cable fatigue, motor synchronization, slow speed, poor corrosion resistance, and power supply issues are a short list of issues with current products. Cable fatigue is in a guaranteed failure mode if cables are not replaced every 2-3 years, depending on frequency of use. All of the designs on the market use wire rope. The galvanized poles used in these designs cause rapid fatigue of the cables because of the small winding diameter. Compounding the issue is the large lift height requirement for most installations. It is common to lift the boat 6-10′ to accommodate the fluctuating water heights. This requires many winds on the pole and in most cases, the cable winds over itself. This not only fatigues the cable, but also damages the individual wires with the wire rope.
Cable failure modes are severe and cause the boat to fall in one direction endangering people and equipment. The most common approach to avoiding this failure is to replace cables often.
Motor synchronization is also an issue in multi-pole/motor setups. Piling mount systems have at least two motors because there is no overhead structure to route cables to a single pipe. The speed of the motors will vary causing one to lift faster or slower than the other. Most systems require the user to use a switch to momentarily shut off one of the motors to allow the slower motor(s) to catch up. This requires constant user attention when lifting or lowering the boat. Compounding this issue is the slow speed of the pole winding systems. Some lifts can take over 6 minutes to lift the boat to the needed elevation above the water.
The galvanized construction of the pole winding systems is adequate for most environments, but they eventually rust as the wound areas of the poles lose their zinc coating. The bearing locations are generally welded components. Aluminum or other naturally corrosion resistant materials are avoided because of the high stresses in these areas. Cable materials are often galvanized also due to the high replacement rate. The cable will be replaced due to fatigue before corrosion becomes an issue.
Pole-winding systems are predominately A/C power systems. Piling mount systems require a long supply from the dock to the opposite motor. This can often be a 40-50′ length of cord to run down from the dock, tinder the water, and back up to the opposite motor. This length is too long for a DC (12-24V) power supply to run without extremely heavy wire. The length of the circuit from the supplying A/C panel to the motors is also very long. This often creates a large voltage drop along the circuit. The voltage drop can cause the system to malfunction and reduce the life of the motor(s) in the system. Often new installations require new circuits to be installed with heavier cable.
A/C power can be dangerous system in wet environments. GFCI (ground fault circuit interrupts) are and absolute requirement on docks. Many lives have been lost due to damaged A/C circuits causing stray A/C currents in lakes and waterfronts with inadequate circuit protection. Pole winding systems are commonly used primarily because they can be easily installed in most existing structures with little modification and they are inexpensive when compared to floating or free-standing lift designs.
The vast majority of floating lift systems are called “Air Displacement” systems. Air displacement systems raise and lower a lift structure using floats. The floats are filled with air that is evacuated to allow the structure to sink. The floats are then filled using vacuum pumps to raise the structure with the boat on it.
Floating systems such as U.S. Pat. No. 6,823,809 to Hey have a few advantages over free standing and mounted lift structures. They can be used in very deep water where pile mounted systems are not an option. They can also be used in dockominium structures where a very limited structural connection is available.
U.S. Pat. No. 6,823,809 to Hey shows a boat lift that mechanically lifts the boat using a unique linkage to lift the boat without requiring air evacuation. This hydraulic system is innovative, but expensive. The system also places critical hydraulic components at the waterline. This jeopardizes the durability of the system. Those boat hoists do not require any structural connection to the pier and can be moored similarly to the boat.
But air displacement lifts require a mounted structure on the dock. As air is evacuated from the floats gravity will cause the structured to sink to the lakebed unless a structure is in place to limit the travel. This lift style does not work well in shallow areas because of the size of the floating structure.
Lift capacity of floating lift systems is determined by the amount of flotation. The float structure is also designed to allow the structure to lift the boat sufficiently above the water. As the lift capacity increases, the number of air chambers increases. Larger structures require the user to evacuate the chambers at different rates to ensure a balanced movement. Users often complain about this requirement and the difficulty controlling it.
U.S. Pat. No. 6,976,442 to Hey and U.S. Pat. No. 7,246,970 to Hey show boat lifts that use a cantilever method to lift the platform. The lift will be in the elevated position most of the time, so that in these systems, the rod surface spends most of its life exposed to the harsh marine environment. This can cause corrosion and pitting of the rod surface which will cause leaking of the hydraulic seals.
Accordingly, there is a need for a boat lift for pilings and boat houses that will overcome the aforementioned problems.